Liquid fuel supply apparatus



Dec. 16, 1952 J. K. HARDING LIQUID FUEL SUPPLY APPARATUS 2 SHEETS-SHEET l Filed Deo. 26, 1950 mwN@ SEER@ /MN INN NN IFN WN Inventor M D M H Y.

m, 4 my Attorneys Dec. 16,*1952 J. K. HARDING 2,621,599

LIQUID FUEL SUPPLY APPARATUS Filed Dec. 26, 19.50 v 2 SHEETS-SHEET 2 mi l /VOEMAL FUN/VIN@ 5mm/N6, 55cm/D .STAGE Inventor JOHN K. HARD/N6 (72g y g., ,3 l r @www Atorn eys Patented Dec. 16, 1952 LIQUID FUEL SUPPLY APPARATUS J h11 K. Harding, Cheltenham, England, assigner to Dowty Equipment Limited, Arle Court, Cheltenham, England Application December 26, 1950,Serial-No. 202,704 In Great Britain September 16, 1949 4 claims. (ci. 10s- 42) This invention relates to liquid fuel feed control apparatus intended more particularly for supplying varying quantities of fuel to the burners of an internal combustion turbine engine suitable for aircraft propulsion. The invention is concerned with such apparatus comprising an engine-driven fuel pump which operates normally as a fixed displacement pump and has associated with the outlet thereof a return by-pass the effectiveness of which is controlled by a pressurebalanced piston by-pass valve which accommodates itself automatically in accordance with variable factors including the setting of a variable restriction or throttle in the supply line to the burners, said by-pass valve thereby maintaining a constant pressure in the line to the throttle, or a constant pressure drop across the throttle. The piston by-pass valve has opposed .pressure faces of which that nearer the valve seating is hereinafter referred to as the inner face and of which that remote from the seating is hereinafter re'- ferred to as the outer face. The inner face is, during all self-running conditions of the engine, exposed to the pressure of fuel in the delivery line from the pump, and the outer face is exposed to the pressure of fuel which has passed from said delivery line and through a fixed restriction or metering orifice. The outer face is also in communication with a relief or vent valve the closure member of which is controlled by means responsive to any suitable engine-controlling variable or derivative thereof, in order to govern the position of the by-pass valve. Such apparatus is hereinafter referred to as "liquid fuel feed control apparatus of the kind hereinbefore specified.

All the while the engine is running normally, excepting possibly during rapid accelerations, the by-pass valve will be in an open position, and during starting-up of the engine it is desirable for this valve to be in its closed position so that fuel initially delivered by the pump will not be by-passed until the pump is delivering more than the engine needs. In meeting this requirement it has been customary with this type of valve to provide a spring which biases the valve towards its closed position, said spring action being overcome by the pressure of the fuel during normal engine running. These by-pass valves have to exercise a delicate control over the Vby-pass and it is believed that the presence of the spring interferes to some extent with the sensitivity of the valve during normal engine running. Moreover, the presence of the spring places a limit to the minimum pump delivery pressure, which in some circumstances may be unduly high. It is therefore consideredI desirable to free the by-pass valve from all spring restraint, and the present invention seeks to provide improved apparatus whereby this can be achieved without introducing difficulties during the process of starting the system.

In liquid fuel feed control apparatus of the kind hereinbefore specified, according to the present invention the pressure-balanced piston bypass valve is slidable in its housing wholly under iiuid pressure inuence, and the part of the bypass passage between the pump outlet and the inner pressure face of the by-pass valve includes a spring-biased valve (hereinafter referred to as the pressurising valve) which, when the system is dead, engages its seating to close the said part of the by-pass passage, and which moves and remains away from its'seating whenever a predetermined delivery pressure is exceeded.

Whenl the engine starts to turn, the pressurising valve and the relief or vent valve will be closed, and the by-pass valve may be in an open position. Fuel initially delivered by the pump will be able to flow through the fixed restriction to the outer .pressure face of the by-pass valve and as far as the relief or vent valve. The pressurising valve prevents fuel from reaching the inner face of the by-pass valve. The fuel pressure now acting upon the outerface of the bypass valve shifts the latter into its closed position. The pressure build-up which immediately follows will be sufficient to unseat the pressurising valve so that fuel can now also reach the inner face of the by-pass valve. The by-pass valve will remain in its closed position until, soon after the pressurising valve has unseated and moved against an outward limit stop, the fuel pressure has builtup further to open the relief or vent valve. There will now be a continuous flow through the xed restriction with consequent pressure drop which occurs at the outer face ofv the by-pass valve with the result that the bypass valve moves to open the by-pass until it reaches a position of equilibrium as determined by the relief or vent valve.

The pressurising valve and its spring loading are such that the pressurising valve unseats before the engine obtains self-running conditions and will remain unseated until the engine, in stopping, passes below its idling speed.

A supply line from the .pump outlet to the burners may lead from the pump side of the pressurising valve, or from the space between the pressurising valve and the inner pressure face of the by-pass valve.

In order that the invention may be more clearly understood and readily carried into effect, liquid fuel feed control apparatus in accordance with the preferred embodiment thereof will now be described with reference to the accompanying sectional drawings, Of WhCh Figure 1 shows the parts with the engine et rest; Figures 2 and 3 show the parts during successive stages of starting the engine; and Figure 4 shows the parts during a normal running condition of the engine.

As shown, a fuel inlet passage i I in a casing I2 communicates through ports I3 with the inlet of an engine-driven fuel pump of the xed displacement type. The pump itself has not been illustrated. The outlet side of the pump delivers fuel through a port I4 from which the fuel can now along a delivery line I5. There is a return by-pass passage between the outlet port i4 and the inlet ports I3, said by-pass passage comprising duct I6, space Il, holes I8, annular space I9. slot and space 2I. A fitting 22 is secured in a liquid-tight manner in the casing I2 and the ntting forms a cylinder for the piston 23 of a bypass valve 24 which is of the pressure-balanced type. The by-pass valve 24 has a stem 25 which is formed with the slot 2c and extends through an annular seating 26. The stem 25 of the bypass valve has longitudinal grooves 2l whereby the space I9 communicates with the space 28 at the inner face of the piston 23. A conduit 29 including a restrictor 30 places the delivery line I5 in communication With the space at the outer face of the piston 23. Said space is also in communication through a conduit 3l with a relief or vent valve of any known or convenient type (not shown). The conduit 29 and restrictor 38 are, for clearness, shown outside the casing I2 and tting 22, but in practice they would probably be formed internally thereof. The duct I6 has an axially directed annular seating 32 at its lower end with which engages the upper end of a pressurising valve 33 which is loaded to tend to engage the seating 32 by a light spring 34. The chamber 35 housing the spring 34 communicates with the inlet passage I I by way of a port 35, annular space 31, and duct 38 which leads from said space to the passage II. The chamber 35 may alternatively be open to atmosphere or to some other source of low pressure, the objective being merely to avoid trapping a fluid within the space 31, and thereby impeding unseating of the valve 33 when required.

When the engine is at rest and the system is dead the pressure-balanced by-pass valve 24 will most likely be in an open position such as shown in Figure l, and the pressurising valve 33 will be in its closed position as shown in the gure.

When the engine starts to turn during the starting-up operation of the engine, fuel delivered by the pump will flow through the port Id and into the delivery line I5. It will also ow along the duct I6 as far as the pressurising valve 33, and along the conduit 29 to the outer face of the piston 23, and along the conduit 3I as far as the closure member of the relief or vent valve. The fuel pressure acting upon the outer face of the by-pass valve 24 will lift said valve into its closed position, as shown in Figure 2. The pressure build-up in the duct I6 will soon be sulicient to overcome the spring 34 of the pressurising valve which latter Will move down against its limit stop, as seen in Figure 3. The by-pass valve 24 will still be in its closed position and the relief or vent valve will also stiil be closed. Next, the pressure in the conduit 3I will be sufficient to cause the relief or vent valve to open to some extent and a continuous flow of fuel will now take place across the restriction 30. This will bring about a pressure drop which will reduce the pressure at the outer face of the piston 23 with the result that the by-pass valve 24 will move correspondingly to open the by-pass passage, as seen in Figure 4. The engine will now have achieved a self-running condition and the flow along the by-pass passage Will be governed by ythe position of the by-pass valve 24. The by-pass valve 24 is itself governed by the extent of opening or closing of the relief or vent valve in known manner. It will be seen that the by-pass valve 24 is freed from all spring restraint yet is caused to assume its closed position during the initial stages of starting the engine and before the engine has achieved a self-running condition. All the While the engine is operating normally, the pressurising valve 33 will be in its open position shown in Figures 3 and 4, and will remain in this position until the engine, in stopping, passes :below its idling speed. After the closure member of the relief or vent valve has closed said valve, the fuel pressure in the duct I5 will drop sufficiently to permit the pressurising valve 33 to re-engage its seating 32 under the infiuence of its spring 34 in readiness for a fresh starting-up operation of the engine.

Freeing the by-pass valve 24 from spring restraint not only enhances the sensitivity of control but permits of lower pump delivery pressures than would otherwise be possible.

I claim:

1. Liquid fuel feed control apparatus for the use specified, including a supply line; a delivery line which under operating conditions is pressurised; a housing constituting part of a by-pass duct interconnecting said supply and delivery lines; a pressure-balanced by-pass valve, including a pressure-sensitive element shiftable, in said housing, with the valve itself, and exposed at each face to and operable Wholly under the influence of fluid pressures, to regulate now through said by-pass duct, and by such shifting to assume a position of rest in the absence of delivery pressure, and denite control positions corresponding to definite operating pressures; a pressure duct leading from said delivery line to a point of communication at all times with one face of the pressure-sensitive element, to urge the latter and the by-pass valve in the closing sense into a controlled position during existence of delivery pressures; a pressurizing valve interposed in that part of said by-pass duct which is intermediate said delivery line and said by-pass valve, and having one face exposed to delivery pressure; the opposite face of said pressure-sensitive element under operating conditions being in communication with that portion of the by-pass duct Which is intermediate the two valves and resilient means biasing the pressurising valve to a closed position, but yieldable to and upon the attainment during operation of a pressure in the delivery line, applied to the exposed face of the pressurising valve, which is in excess of a predetermined pressure, whereby said pressurising valve is opened, and is held open during normal operation, for access of pressure to said opposite face of nthe pressuresensitive element, thereby to urge the latter and the by-pass valve in the opening sense into a regulating position that is dependent upon the pressures applied to 4the respective faces of the pressure-sensitive element, but remains closed at starting up until the attainment in the delivery line of such predetermined pressure.

2. Liquid fuel feed control apparatus as lin claim 1, including a vent communicating between that face of the pressurising valve which is opposite the exposed face of the latter, and a space having always a pressure lower than any pressure existing in the delivery line during operation.

3. Liquid fuel feed control apparatus as in claim 1, wherein the pressure-sensitive element comprises a. piston, and the housing includes a cylinder wherein the piston is reciprocable, said piston being directly connected to and slidable with the by-pass valve.

4. Liquid fuel feed control apparatus as in claim 1, including a restriction interposed in the pressure duct intermediate the delivery line and the point of communication with the one face of the pressure-sensitive element.

JOHN K. HARDING.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name D ate 1,868,444 Bechtold July 19, 1932 .2,173,578 Egersdorfer et al. Sept. 19. 1939 

